Synchronicity

The case for a new transmission for the 2008 Viper SRT10® was summed up succinctly by Kevin Stepinski, senior product engineer for SRT® and the person mainly responsible for the Viper drivetrain. “We used to say about the old transmission, ‘You shift the T56 because you have to, not because you want to,’” he explained.

The new TR6060 transmission is the latest evolution of the Tremec T56 six-speed manual that Viper owners know and (conditionally) love. The T56 got the job done, but most Viper owners found it not to be as crisp with its shifting as they would have liked. The folks at SRT knew that if they were going to move the 2008 Viper along toward the 600 hp mark, they would need a new transmission that would be equal to the task.

The TR6060 is more than capable of delivering on that promise. Stepinski pointed out that, although they may look similar, the TR6060 has almost totally different components than the T56. He explained, “There may be two or three parts that are the same, but for the most part, it’s all new. Two of the biggest changes are the wider gears for higher torque capacity and a new synchronizer package.”

The new shifter system results in greatly improved performance. Stepinski said, “The shifter throws are 20 percent shorter than the T56. Going from first to second has been reduced by three-quarters of an inch. That’s a dramatic improvement. The TR6060 is the whole package—there is less free play, reduced shift travel and more shift precision.”

But improved shift quality is just part of the story behind the new TR6060. And part of the development history involves a couple of the Dodge Viper’s archrivals—the Chevrolet Corvette and the Ford GT.

Share and Share Alike

The research, testing and development cost that goes into a major component such as a transmission can be daunting—especially when the expense can only be spread out over a limited production such as the Viper’s.

Stepinski said that as SRT was planning to revamp the trans for the Viper, Tremec was already doing work on an upgrade for Ford and Chevy. “We all shared the design and production cost for the TR6060,” he pointed out. “It not only helps keep the overall cost down, it means we can devote more resources to other parts of the Viper.”

The objectives of the new transmission were simply stated, but certainly easier said than done:

• Support increased torque levels of the new 8.4 liter engine
• Meet durability standards
• Improve shift precision
• Improve driveability and ergonomics

“In order to accomplish these goals, everything had to be re-evaluated and redesigned,” Stepinski said. “One of the biggest changes was in the synchronizer designed. The old T56 had a double cone for 1–2 and a single cone for 3–6. The TR6060 has a triple cone for 1–2 and a double cone for 3–6. These enhancements reduce friction and improve engagement feel.”

Of course, the changes didn’t stop there. The TR6060 has gears that are 10 percent wider than its predecessor which gives the new trans a higher torque capacity. The shorter travel of the synchronizers makes extra space available for the use of stronger, wider gears.

The addition of wider gears is made possible through the use of special fine-pitch teeth synchronizers. Stepinski said, “Basically it means that there are now three teeth where there used to be two. This enables the driver to make quicker shifts. Skip shift and reverse solenoids are similar to the T56, but the heavier springload keeps you from shifting into reverse when you don’t want to.”

The TR6060 is 10mm longer than the T56 and the front adaptor is thicker. There is also improved case structural thickness which improves stiffness. The shifter has also been rotated forward to compensate for the extra length. The front cover casting has been strengthened with a larger input shaft bearing. “Some of these changes contributed to increased weight (the TR6060 is six pounds heavier than the T56) and, although this is not desirable, in this instance we think it was definitely worthwhile,” Stepinski explained.

More Drivetrain Enhancements

Throwing in a new transmission without reworking the rest of the drivetrain would not give SRT the performance improvements it was looking for. So there was a lot more work to be done.

The clutch and flywheel first came under close scrutiny. A small diameter, low inertia Sachs twin-disc design replaced the old large diameter single-disc clutch. The smaller, more compact design resulted in an 18 percent reduction in rotating inertia.

Torque capacity is more than 600 lb-ft and the improved design leads to reduced clutch pedal efforts and improved engagement feel. The clutch hydraulic system uses a revised slave cylinder mated to a clutch master cylinder and adjustable pedals, so the driver can achieve maximum performance and comfort.

The 2008 Viper SRT10 propshaft has a new larger slip yoke—from 47.879mm–47.904mm, although the overall length is the same as the 2003–2006 model years. The old yoke was 42.659mm–42.710mm.

There is also an all-new GKN ViscoLok speed sensing rear differential. With its 4-pinion design, the ViscoLok diff has a viscous shear pump and the sealed unit means quicker response time and fewer temperature effects. Stepinski pointed out, “Overall, the GKN differential gives the Viper faster response to traction transients, progressive and linear lockup characteristics under limited handling conditions and improved corner exit traction. In other words, it provides excellent vehicle dynamics characteristics.”

Stepinski added, “With this new differential, there’s an extremely quick response time. There’s no one-wheel peel, no delay and no leakage. It grips, it’s fast—so you better be ready.”

The 6-speed TR6060 uses Mopar® ATF+4® lubricant and is certified “fill-for-life,” requiring no fluid changes. The clutch is activated hydraulically, which automatically compensates for clutch disc wear, eliminating manual adjustments. The lower viscosity means there is reduced parasitic loss and it runs cooler. The Tremec TR6060 has evolved to a point that it requires virtually no maintenance in all but the most severe conditions.

And there’s even more good news about the TR6060 transmission—it’s not just for 2008 and beyond Vipers. Stepinski explained, “With just a few modifications, the TR6060 will fit in the 2003–2006 Vipers. Mopar is coming up with a kit next year, starting with the flywheel—so that it will be easy for anyone interested to make the switch. It should just drop right in.”